Surface plasmon four-wave mixing microscopy

Abstract

Laser pulses are applied to surface plasmon resonant articles such as gold nanoparticles within a microscopy sample to generate a four-wave mixing signal that is detected as the output of the microscopy process.

The invention claimed is: 
     
       1. A microscope comprising:
 an illumination source arranged to illuminate a sample zone with stimulation light that is absorbed by a marker, if present in the sample zone, and is emitted as four-wave mixing light, and 
 a detector arranged to discriminate the four-wave mixing light in light emanating from the sample zone, 
 wherein the illumination source comprises:
 a light source that emits a train of pulses of laser light, and 
 an arrangement of parallel optical paths configured to received said train of pulses, and 
 
 wherein said arrangement of parallel optical paths is configured to:
 create first, second and third versions of a single pulse of said train of pulses, and 
 deliver said first, second and third versions of said single pulse to the sample zone such that the third version arrives at the sample zone after the second version and the second version arrives at the sample zone not earlier than the first version and not later than the first version by more than the dephasing time of the marker, and 
 
 wherein the detector is configured to bring a fourth version of the said single pulse into interaction with the light emanating from the sample zone and the detector is configured to detect interference of the fourth version of said single pulse with four-wave mixing light triggered by the third version of said single pulse. 
 
     
     
       2. The microscope according to  claim 1 , wherein the illumination source is arranged to deliver said first and second versions of said single pulse to the sample zone at the same time. 
     
     
       3. The microscope according to  claim 1 , further comprising a frequency modulator arranged to cause the first, second and third versions of said single pulse to be displaced in frequency relative to one another. 
     
     
       4. The microscope according to  claim 3 , wherein the frequency modulator is arranged to use acousto-optic modulation to displace the first, second and third versions of said single pulse relative to one another in terms of frequency. 
     
     
       5. The microscope according to  claim 1 , wherein said arrangement of parallel optical paths comprises first and second delivery paths, the first path is arranged to deliver the first and second versions of said single pulse to the sample zone and the second path is arranged to deliver the third version to the sample zone. 
     
     
       6. The microscope according to  claim 5 , wherein at least the first path comprises a respective acousto-optic modulator. 
     
     
       7. The microscope according to  claim 6 , further comprising a signal generator for driving the acousto-optic modulator in the first path with a signal that modifies said single pulse into said first and second versions. 
     
     
       8. The microscope according to  claim 1 , wherein said arrangement of parallel optical paths comprises first, second and third delivery paths, the first path is arranged to deliver the first version of said single pulse to the sample zone, the second path is arranged to deliver the second version to the sample zone and the third path is arranged to deliver the third version to the sample zone. 
     
     
       9. The microscope according to  claim 8 , wherein at least two of the first, second and third paths comprise a respective acousto-optic modulator. 
     
     
       10. The microscope according to  claim 1 , wherein the marker is a surface plasmon resonant gold particle. 
     
     
       11. The microscope according to  claim 1 , wherein the marker is a dimer. 
     
     
       12. The microscope according to  claim 1 , wherein said light source is a laser. 
     
     
       13. A method of performing microscopy on sample material, the method comprising:
 illuminating the sample material with stimulation light that will be absorbed by a marker and will be emitted as four-wave mixing light; and 
 discriminating the four-wave mixing light in light emanating from the sample zone; 
 wherein illuminating the sample material comprises:
 emitting a train of pulses of laser light, and 
 receiving said train of pulses in an arrangement of parallel optical paths, and 
 
 wherein said arrangement of parallel optical paths is configured to:
 create first, second and third versions of a single pulse of said train of pulses, and 
 convey first, second and third versions of said single pulse of laser light to the sample zone such that the third version arrives at the sample zone after the second version and the second version arrives at the sample zone not earlier than the first version and not later than the first version by more than the dephasing time of the marker, 
 
 wherein the method further comprises: 
 bringing a fourth version of said single pulse into interaction with the light emanating from the sample zone, and 
 wherein discriminating the four-wave mixing light comprises: 
 detecting interference of the fourth version of said single pulse with four-wave mixing light triggered by the third version of said single pulse. 
 
     
     
       14. The method according to  claim 13 , further comprising applying the stimulation light again at higher power such that sufficient energy is absorbed into a surface plasmon of the marker to disassociate the marker from the sample material. 
     
     
       15. The method according to  claim 13 , wherein said arrangement of parallel optical paths is configured to convey said first and second versions of said single pulse to the sample zone at the same time. 
     
     
       16. The method according to  claim 13 , further comprising adjusting the first, second and third versions of said single pulse to be displaced in frequency relative to one another. 
     
     
       17. The method according to  claim 13 , wherein said light source is a laser. 
     
     
       18. The method according to  claim 13 , wherein the marker is a surface plasmon resonant gold particle. 
     
     
       19. The method according to  claim 13 , wherein the marker is a dimer. 
     
     
       20. A method of performing microscopy on a sample material having at least one surface plasmon resonant marker attached thereto, the method comprising optically imaging the sample material and using a result to select a region of the sample material for imaging via electron microscopy, wherein the optically imaging the sample comprises:
 illuminating the sample material with stimulation light that will be absorbed by a marker and will be emitted as four-wave mixing light and 
 discriminating the four-wave mixing light in light emanating from the sample zone, 
 wherein illuminating the sample material comprises:
 emitting a train of pulses of laser light, and 
 receiving said train of pulses in an arrangement of parallel optical paths, and 
 
 wherein said arrangement of parallel optical paths is configured to:
 create first, second and third versions of a single pulse of said train of pulses, and 
 convey said first, second and third versions of said single pulse to the sample zone such that the third version arrives at the sample zone after the second version and the second version arrives at the sample zone not earlier than the first version and not later than the first version by more than the dephasing time of the marker, 
 
 wherein optically imaging the sample further comprises: 
 bringing a fourth version of said single pulse into interaction with the light emanating from the sample zone, and 
 wherein discriminating the four-wave mixing light comprises: 
 detecting interference of the fourth version of said single pulse with four-wave mixing light triggered by the third version of said single pulse.